As a system in which a station-side communicating apparatus connected to a communication network performs one-to-N communication with a plurality of subscriber devices via a time-division-multiple-access (TDMA) line to connect the subscriber devices to the communication network, there are various communication systems, such as a wireless communication system, a passive optical network (hereinafter, “a PON system”), and a local-area-network (LAN) system. In this type of communication system, an upload bandwidth that is used by the subscriber devices to transmit packet data to the station-side communicating apparatus is shared by the subscriber devices.
Various methods have been proposed for the station-side communicating apparatus to allocate the upload bandwidth in response to bandwidth requests from the subscriber devices and according to service levels of the subscriber devices. The first literature Japanese application patent laid-open publication No. 2001-53711, for example, discloses the bandwidth allocation method in the wireless communication system. The second literature “Dynamic Bandwidth Allocation Algorithm for GE-PON (International Conference on Optical Internet ((OJN2002))”, for example, discloses the bandwidth allocation method in the PON system. The third literature Japanese application patent laid-open publication No. 2000-244527, for example, discloses the bandwidth allocation method in the LAN system.
For easy understanding of the present invention, the conventional dynamic bandwidth-allocation method will be described below (FIGS. 1 to 4) with reference to the PON system disclosed in the second literature. Note that because the second literature does not clearly specify the transmission type, the description below uses the transmission type disclosed in the third literature. FIG. 1 is a block diagram for illustrating a general configuration of the PON system. FIG. 2 is a block diagram for illustrating an example of a configuration of a subscriber terminating apparatus shown in FIG. 1. FIG. 3 is a block diagram for illustrating an example of a configuration of a portion of a station-side communicating apparatus shown in FIG. 1, which relates to a bandwidth allocation. FIG. 4 is a flowchart of a processing procedure for a conventional dynamic bandwidth-allocation method.
As shown in FIG. 1, the PON system includes a station-side communicating apparatus 1, and a plurality of subscriber devices (hereinafter, “subscriber terminating apparatuses”) 2a, 2b, and 2c. The subscriber terminating apparatuses 2a, 2b, and 2c connect to the station-side communicating apparatus 1 through an optical transmission path (optical fiber 3, optical coupler 4, and optical fibers 5a, 5b, and 5c). More specifically, the optical fiber 3 connected to the station-side communicating apparatus 1 is divided into a plurality of optical fibers 5a, 5b, and 5c at the optical coupler 4. The optical fibers 5a, 5b, and 5c connect to the subscriber terminating apparatuses 2a, 2b, and 2c, respectively. The station-side communicating apparatus 1 connects to a network 6. The subscriber terminating apparatuses 2a, 2b, and 2c connect to, for example, terminal devices 7a, 7b, and 7c, respectively.
The station-side communicating apparatus 1 exchanges packet data with the subscriber terminating apparatuses 2a, 2b, and 2c through the TDMA line. During each data-collection cycle, the station-side communicating apparatus 1 obtains request data amount sent from the subscriber terminating apparatuses 2a, 2b, and 2c. According to the request data amount, the station-side communicating apparatus 1 allocates the upload bandwidth to each of the subscriber terminating apparatuses 2a, 2b, and 2c. The station-side communicating apparatus 1 can set the contract bandwidth for each of the subscriber terminating apparatuses 2a, 2b, and 2c. 
Each of the subscriber terminating apparatuses 2a, 2b, and 2c includes a buffer memory unit 22 that stores the packet data input from a terminal device. The subscriber terminating apparatuses 2a, 2b, and 2c inform the station-side communicating apparatus 1 of the data amount accumulated in the buffer memory unit 22 as the bandwidth request. When each of the subscriber terminating apparatuses has a plurality of terminal devices connected thereto, it includes a buffer memory unit for each of the terminal devices, and informs the station-side communicating apparatus 1 of the accumulated data amount in each buffer memory unit.
As shown in FIG. 2, the subscriber terminating apparatus 2 includes a data receiving unit 21, the buffer memory unit 22, a data-amount counter unit 23, a control-signal generating unit 24, a transmission-timing adjusting unit 25, and a data transmitting unit 26.
The data receiving unit 21 stores the packet data input from the terminal device in the buffer memory unit 22. The data-amount counter unit 23 counts data amount stored in the buffer memory unit 22 and informs the amount to the control-signal generating unit 24. The control-signal generating unit 24 uses the data amount counted by the data-amount counter unit 23 as a basis to generate a control signal for a request to the station-side communicating apparatus 1 for the bandwidth. The data transmitting unit 26 transmits the control signal to the station-side communicating apparatus 1 at the timing specified by the transmission-timing adjusting unit 25. The data transmitting unit 26 also transmits the packet data accumulated in the buffer memory unit 22 to the station-side communicating apparatus 1. The data transmitting unit 26 transmits the packet data in the order in which the data is stored in the buffer memory unit 22 at the own transmission timing specified by a transmission-timing adjusting unit 55.
In this manner, the subscriber terminating apparatus 2 can inform the station-side communicating apparatus 1 of the request data amount by transmitting the control signal. The subscriber terminating apparatus 2 can also transmit the packet data input from the terminal device to the station-side communicating apparatus 1.
As shown in FIG. 3, the station-side communicating apparatus 1 has a configuration for the dynamic bandwidth-allocation. The configuration includes a control-signal receiving unit 30, a request-data-amount collecting unit 31, an allocation determining unit 32, a bandwidth adjusting unit 33, a transmission-permission-signal generating unit 34, and a control-signal transmitting unit 35. The station-side communicating apparatus 1 dynamically allocates the upload bandwidth in the sequence shown in FIG. 4. According to FIG. 4 and referring to FIG. 3, a description is given of how the station-side communicating apparatus 1 dynamically allocates the upload bandwidth.
As shown in FIG. 4, the control-signal receiving unit 30 receives the control signal which includes the stored data amount transmitted by the subscriber terminating apparatus. After receiving the control signal, the control-signal receiving unit 30 informs the request-data-amount collecting unit 31 of the stored data amount of the subscriber terminating apparatus that is indicated in the control signal. The request-data-amount collecting unit 31 thus collects the request data amount from all the subscriber terminating apparatuses (step ST1).
For the request data amount from each subscriber terminating apparatus held in the request-data-amount collecting unit 31, the allocation determining unit 32 sequentially determines the allocation (step ST2) in the determination order previously set by the bandwidth adjusting unit 33. The allocation determining unit 32 determines the allocation by determining whether the allocation to the selected subscriber terminating apparatus #n causes the total allocation amount more than a bandwidth-allocation amount previously set per one bandwidth-update cycle (step ST3).
If the allocation is possible to the selected subscriber terminating apparatus #n (“NO” at step ST3), the allocation determining unit 32 permits the allocation to the subscriber terminating apparatus #n, and informs the transmission-permission-signal generating unit 34 of the request data amount as the transmission-permitted amount (step ST4), then the flow proceeds to step ST5.
At step ST5, the allocation determining unit 32 determines whether the allocation is completed for all the subscriber terminating apparatuses. Until the allocation is completed for all the subscriber terminating apparatuses (“NO” at step ST5), the allocation determining unit 32 performs the allocation to all the subscriber terminating apparatuses by repeating the process from step ST2 to step ST4. If the allocation is completed for the entire subscriber terminating apparatuses (“YES” at step ST5), the flow proceeds to the operation of the transmission-permission-signal generating unit 34 (step ST6).
In repeating the processes from step ST2 to step ST4, if the allocation is not performed to the selected subscriber terminating apparatus #n (“YES” at step ST3), the allocation determining unit 32 informs accordingly the transmission-permission-signal generating unit 34. The allocation determining unit 32 then stops the allocation determination to the subscriber terminating apparatus #n, then the flow proceeds to step ST6. This means that a subscriber terminating apparatus occurs which does not receive the allocation determination.
The transmission-permission-signal generating unit 34 generates the transmission-permission-signal which indicates the transmission-permitted amount informed from the allocation determining unit 32. The control-signal transmitting unit 35 transmits the transmission-permission-signal to the subscriber terminating apparatus to which the allocation is permitted (step ST6). If there is a subscriber terminating apparatus to which the allocation is not performed, the transmission-permission-signal generating unit 34 informs accordingly that subscriber terminating apparatus.
Based on the data amount which is determined to be allocatable by the allocation determining unit 32 and on the contract bandwidth of the each of the subscriber terminating apparatuses, the bandwidth adjusting unit 33 determines (or updates) the order in which the next allocation determination is performed (step ST7). The above-described bandwidth-update cycle is the cycle during which the bandwidth adjusting unit 33 determines (or updates) the order in which the allocation determination is performed.
The dynamic bandwidth-allocation method in the conventional technology can periodically perform the set of the processes shown in FIG. 4 and can dynamically allocate the bandwidth according to the bandwidth request from each subscriber terminating apparatus. If more bandwidth is allocated to the subscriber terminating apparatus than its contract bandwidth, its allocation order can be postponed as lower priority in the next allocation determination, thereby limiting the bandwidth allocation. If less bandwidth is allocated, on the other hand, to the subscriber terminating apparatus than its contract bandwidth, its allocation order can be brought forward as higher priority in the next allocation determination, thereby increasing the bandwidth allocation.
The dynamic bandwidth-allocation method in the conventional technology can set the data amount requested from each subscriber terminating apparatus as the transmission-permitted amount to eliminate the useless bandwidth allocation, thereby making it possible to effectively use the bandwidth shared by the subscriber terminating apparatuses.
In the dynamic bandwidth-allocation method in the conventional technology, however, if a plurality of subscriber terminating apparatuses provides a large request data amount, an allocation permitted to a small number of subscriber terminating apparatuses may cause the total allocation amount more than a bandwidth-allocation amount per one bandwidth-update cycle, permitting no allocation to the remaining subscriber terminating apparatuses. Some subscriber terminating apparatuses have thus less opportunity for allocation, thereby increasing the time for the packet data input from the terminal device to be output from the subscriber terminating apparatus.
To solve the above-described problems, it is readily inferred that a portion of each request data amount may preferably be allocated. In this case, however, the station-side communicating apparatus needs to determine the transmission-permitted amount without considering the delimitation in the variable-length packet data which is stored in the buffer memory unit in the subscriber terminating apparatus. When the station-side communicating apparatus determines the transmission-permitted amount for each subscriber terminating apparatus without considering the delimitation in the variable length packet, the subscriber terminating apparatuses need to separate the variable-length packet data stored in the buffer memory unit to use all of the allocation permission. The station-side communicating apparatus needs a means for differentiating the separated packet data and non-separated packet data and a means for recombining the separated packet data. A problem thus arises in which redundant functions have to be added to the station-side communicating apparatus and subscriber terminating apparatus.
To transmit the packet data with the same delimitation as that in the variable-length packet data stored in the buffer memory unit, the subscriber terminating apparatuses need to use not all the transmission-permitted amount. The subscriber terminating apparatuses alternatively need to use only a portion of the transmission-permitted amount that allows the transmission of the packet data amount without separating it. In this case, the remaining portion of the transmission-permitted amount is unnecessary allocation, which may prevent the effective use of the upload bandwidth shared by the subscriber terminating apparatuses.
As described above, the dynamic bandwidth-allocation method in the conventional technology sets the request data amount as the transmission-permitted amount for the purpose of effectively using the shared bandwidth, which leads to a longer data-transmission waiting time of the subscriber terminating apparatuses. On the other hand, increasing the allocation occasions to decrease the data-transmission waiting time may cause a problem in which redundant functions need to be added or unnecessary allocation need to be generated for effectively using the shared bandwidth.
The present invention is accomplished in light of the above-described problems. An object of this invention is to provide a station-side communicating apparatus which can detect packet data delimitation in the request data amount and can allow the allocation for a portion of the request data amount, thereby effectively using the shared bandwidth and allocating the upload bandwidth to decrease the data-transmission waiting time.